Data Security Assignment Case Study

Symmetric and asymmetric ciphers

In this part you will practice encrypting and digitally signing documents. Tasks

Task 2.1 

You are to encrypt your last name using a Caesar cipher, the key for the cipher will be the sum of all the digits of your student number modulo 10. (Modulo 10 means dividing the sum by 10 and taking the remainder as the result.)

NOTE: If your name is hyphenated, just leave out the hyphen.

Example: If my student number is s3333371, I would do (3+3+3+3+3+7+1) % 10 which equals 3 (this is the key I will use for the shift).

You must save the resulting ciphertext in a file called XXXXXXX_task_21.txt (where XXXXXXX is your student number without the “s”) and include it in your submission. No additional text must be included in the file and the cipher should be written in lowercase. There is no need to include the key, since it is derived from the student number; we will compute it automatically when marking.

Task 2.2 

You are to take a SHA256 hash of your student number (without the “s”). 

Example: If my student number is s3333371, the hash (minus the “s”) is 71104d3dce566643dbca7cc0fbcf9949ac053912e125031a666e9eae19b09c19

NOTE: Make sure you include only the student number and nothing else in the hash calculations (e.g. exclude the newline/end of line character).

You must then encrypt this hash using the RSA algorithm with the following public key http://titan.csit.rmit.edu.au/~e09962/sicpub.key 

Hint: We recommend looking at openssl which is installed on all the RMIT Linux servers. Alternatively, you can search for some online tools, and use those.

You must save the plaintext (i.e. the hash) and resulting ciphertext in a file called XXXXXXX_task_22.txt (where XXXXXXX is your student number without the “s”) and include it in your submission. The first line in the file is the plaintext (the hash), and the second line is the ciphertext (the encrypted hash). No additional text must be included in the file. There is no need (or point) in including the public key, as we hold the corresponding private key. 6 / 7

Task 2.3 

You must generate an RSA public/private keypair.

You must then take the same SHA256 hash from task 2.2, but now instead of encrypting it with our public key, you must create a digital signature by encrypting the hash with your RSA private key. 

Hint: We recommend looking at openssl which is installed on all the RMIT Linux servers. Alternatively, you can search for some online tools, and use those.

You must save the resulting ciphertext in a file called XXXXXXX_task_23.txt (where XXXXXXX is your student number without the “s”) and include it in your submission. No additional text must be included in the file. You must also submit your user generated public and private key files; name them XXXXXXXpub.key and XXXXXXXpri.key respectively (where XXXXXXX is your student number without the “s”).

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